1. Field of the Invention
This invention relates to production of cermet compositions wherein particles of a metal or metal alloy, are dispersed in a matrix of a ceramic material, and is particularly concerned with the production of cermet compositions of the above type, having high temperature oxidation resistance, high strength and hardness, and high abrasion and erosion resistance, and particularly designed for use as cermet seals for thermionic converters and diodes, and with the production of high temperature oxidation resistant ceramics particularly useful in the production of such cermet compositions. The invention is also concerned with procedure for producing said cermet and ceramic compositions.
2. Description of the Prior Art
It is known to strengthen high temperature resistant metals by adding ceramic or refractory metal oxides thereto. It is also known to incorporate high temperature resistant metals into ceramic materials or refractory metal oxides, in order to increase adhesion of the ceramic material or refractory metal oxide to a metal substrate, to provide high temperature resistance refractory coatings on such metal substrates.
In my U.S. application Ser. No. 348,422, filed Apr. 5, 1973, there is disclosed a high strength cermet composition comprising a sintered body consisting of high temperature resistant metal or metal alloy particles such as niobium or niobium alloys, coated with and dispersed in a continuous matrix of a ceramic oxide such as alumina, yttria or zirconia, and particularly designed for use as cermet seals for thermionic diodes. Although such cermet compositions have been found to be advantageous, cermets having even higher temperature oxidation resistance for application as seals for thermionic converters are required. Also, cermets having improved hardness, and high abrasion and erosion resistance, coupled with high oxidation resistance are required especially for applications such as the production of turbine blades.
NATURE PHYSICAL SCIENCE, VOLUME 238, NO. 80, Pages 28, 29, July 10, 1972, discloses ceramics obtained by hot pressing mixtures of silicon nitride and alumina to form a single phase solid solution, known as the Si--Al--O--N system.